How Fear Changes What We Hear

How does fear alter memory? A new study reveals that it can literally change our perception, a process that may help researchers better understand post-traumatic stress disorder (PTSD), other anxiety disorders and possibly conditions like autism.

Researchers have long known that fear doesn’t tend to stay restricted to one type of scary experience. For example, the sound of a backfiring car may make a combat veteran dive for cover, even though he knows he’s no longer on the battlefield and even though the sound he heard is different from actual gunfire.

Or a childhood run-in with a vicious German shepherd could translate into a fear of all dogs, even tiny Chihuahuas.

The new research, published in Nature Neuroscience, sought to explore this “generalization” of fear and its connection with learning. Emotional experience typically improves learning — that’s why you remember your first love better than first grade.

But in the case of fear, the brain seems to say “better safe than sorry.” Rather than fine-tuning the connections you make while under the influence of emotion, fear instead reduces your ability to discriminate between potential threats, impairing learning about them.

In the study, led by Rony Paz and his colleagues at the Weizmann Institute of Science in Israel, 25 participants were exposed to either a pleasant or repellant scent in conjunction with a musical tone. The group that was exposed to the pleasant smell rapidly learned which tone signaled the smell and which ones didn’t — and also to distinguish between the predictive tone and similar tones that were slightly higher or lower.

While this group improved their ability to identify the target tone by about 25%, the group that smelled the nasty stuff saw their performance on the task fall by about the same amount. And the more the participants disliked the scent, the worse their performance was. A similar effect was found when the tones were paired with other sounds (like the unpleasant noise of metal scraping against metal). The effect was still measurable a day later.

Interestingly, an earlier study found that in some situations, fear makes sensory discrimination better. The authors write:

[I]t seems reasonable that some stimuli should be better discriminated following aversive learning, such as the smell of a cat versus that of a lion, whereas others are better off not discriminated, such as the roar of one lion versus that of another.

Either way, this research suggests that fear changes not only our reactions to experiences, but also our perceptions of the world itself. It suggests that people with PTSD may literally unable to distinguish perceptually between threatening and non-threatening situations; the same may be true in other anxiety disorders. Some theories of autism also suggest that people with the disorder are more likely than non-autistic people to generalize fear and to learn to fear situations more rapidly.

Understanding how to reduce the generalization of fear, either with behavioral therapies or medications, may help treat people with these various disorders, and possibly allow them to see (and hear) the world as a less threatening place. For others, who knows — it may help us get better at tuning out politicians and scare-mongering media and prevent them from dulling our senses.